Here's something you would think we could all agree on: Rigid parts of the body probably shouldn't go slack. But try asking a SeaWorld spokesperson about the drooping dorsal fins on so many of the park chain's performing male orca, about that mighty Alfalfa spike that in the wild juts out above the water's surface but in captivity so often collapses to black taffy. Scientists speculate that the droop could be due to stress, to diet or to the ludicrous practicalities of life in a cement pond: Maybe these beasts were built for the sea, not for swimming in circles.

An "Ask Shamu" FAQ on SeaWorld's website assures kids that "Neither the shape nor the droop of a whale's dorsal fin are indicators of a killer whale's health or well-being."

That reassurance comes just a couple of sentences after SeaWorld's insistence that "a study of killer whales in New Zealand waters" found that "23% of the wild males had dorsal fins that bent over" — a study that, it turns out, is wildly inconsistent with other surveys.

Another sticky point for SeaWorld, as laid out in the vital, upsetting doc Blackfish: Tilikum, the 12,000-pound bull orca whose big splashes still climax daily shows, has been implicated in three deaths. Human deaths, spread over his three decades of forced performances: Two trainers, twenty years apart, and a drifter who in 1999 apparently hid in the park and dived into the wrong pool. Whether Tilikum killed him is unclear, but what isn't in dispute is that Tilikum bit off the man's genitals and, come morning, was swimming about with the corpse on top of him.

Director Gabriela Cowperthwaite centers the film on the 2010 drowning death of Dawn Brancheau, a trainer whom SeaWorld officials have publicly blamed for what they called an accident. They do not argue that Tilikum didn't kill her, just that the whale is innocent of pulling her into the water in the first place. In the film and in the press, other trainers have rallied to her defense, accusing SeaWorld of having covered up the history of violence in this and other whales. Orca, we're reminded, are deeply social creatures whose identities may be defined by their own communities; dropping a calf into a cage with whales from another community can lead to violence. Making matters worse, whales are smart and feeling enough to be victimized psychologically as well as physically. The head trainer at Tilikum's rinky-dink first park would demand that two orca perform a trick and punish both if one failed. Tilikum's screwups as a showman incurred the wrath of his poolmates, and the young whale often emerged in the morning from their shared too-small holding pen scarred and bloodied.

Much of the film is dedicated to killer whales' "highly elaborated emotional lives." We hear the cries of orca mothers whose children have been sent off to other parks. Trainers who knew Brancheau pore over video of Tilikum's performance just before her death and narrate the small incidents that might have upset the whale. Brancheau ran low on fish yet still kept asking Tilikum to perform. The whale seems not to have heard a reward whistle he had been conditioned to relish and then, frustrated, seems to wallow in that most human of emotions: not being recognized for his work. As he sulks, Brancheau steps near the water to bond with him. You have rarely seen footage this tense.

New OSHA regulations demand that a wall always separate seapark trainers and performing orca. SeaWorld is appealing this, the film reports. Elsewhere, one of Cowperthwaite's talking heads reminds us that this is a problem with an easy solution: In the wild, there is not one recorded incident of a fatal orca attack on a human. The movie is revealing, wrenching and important, a reminder that what feels wrong in our gut — the effort to turn free-roaming and unknowable beasts into caged vaudevillians — is always worth investigating.